Spiral antenna

ABSTRACT

Spiral antenna in which adjacent conductors are three dimensional and composed of spaced segments of a spiral disposed in one plane, the ends of which are joined by conductors disposed in another plane which have lengths greater than the spacing between the ends of the segments, thereby increasing the wire length of the convolutions over that of conductors having convolutions which lie only in one plane.

United States Patent [191 Mosko i 1 SPIRAL ANTENNA [75] Inventor: JosephA. Mosko, China Lake,

Calif.

[73] Assignee: The United States of America as represented by theSecretary of the Navy 221 Filed: Jan. 31, 1968 211 Appl.No.:707,352

n11 3,717,878 [451 Feb. 20, 1973 3,106,714 10/1963 Minerva ..343/792.5

Primary Examiner-Samuel Feinberg Assistant Examiner-Richard E. BergerAttorney-G. J. Rubens, R. Miller and V. C. Muller 57 ABSTRACT Spiralantenna in which adjacent conductors are three dimensional and composedof spaced segments of a spiral disposed in one plane, the ends of whichare joined by conductors disposed in another plane which have lengthsgreater than the spacing between the ends of the segments, therebyincreasing the wire length of the convolutions over that of conductorshaving convolutions which lie only in one plane.

4 Claims, 5 Drawing Figures IIIIIIIIIIIII: 711: VA!

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v'qc,v MULLER ROY MILLER ATTORNEYS.

SPIRAL ANTENNA The invention described herein may be manufactured andused by or for the Government of the United States of America forgovernmental purposes without the payment of any royalties thereon ortherefor.

BACKGROUND OF THE INVENTION As exemplified by US. Pats. No. 2,863,145and No. 2,947,000 to Turner and Marston, respectively, spiral dipoleantennas which respond to wide frequency ratios are now well known andhave the advantage over former rod-type antennas in that they occupyless space. In each of these patents the two conductors are wound in theform of equi-distant spaced spirals having portions which radiate atcertain frequencies. As dis- 'closed by Turner, the circumference of acircle at which response occurs equals one wave length of the particularfrequency, the diameter of the circle thus having the wave lengthdivided by pi. Turner also disclosed that this relationship determinesthe minimum size of a many turn spiral antenna. As will subsequentlyappear, this assumption is valid only if the conductors are simpleconvolutions in a single plane in which the length of a convolution ispi times its diameter.

SUMMARY OF THE INVENTION In the present invention, the total length ofeach conductor forms a spiral, similar to. the patents referred to butthe circumferential length at a given convolution is not a function ofpi since the spiral is formed by winding the conductor in a directionother than planar which increases the length of a convolution beyond therelationship of pi times its diameter. A wave length of conductor maythus be disposed in a considerably smaller diameter, thus reducing thesize of the antenna in some proportion to the added length of conductorover'that of a single planar wound conductor as disclosed in the priorart referred to.

BRIEF DESCRIPTION OF THE DRAWING FIG. P.A. illustrates prior art;

FIG. 1 is an isometric view of a portion of a conductor convolution,illustrating the general principle of the invention in one of itsvarious forms;

FIG. 2 is an elevation of a preferred embodiment of the invention,illustrating the conductors, as viewed from the front of the antenna;

FIG. 3 is a section taken on line 3-3, FIG. 2; and

FIG. 4 is a three-dimensional phantom view of a portion of FIGS. 2 and3.

DESCRIPTION OF GENERAL CONCEPT The detailed description of a preferredembodiment, to follow, may be better understood by first comparing theinventive concept with a spiral antenna having conductors which lie in asingle plane, such as those disclosed in the prior art referred to.

Referring first to FIG. P.A., the circumferential length of a particularconvolution of an Archimedian spiral, as disclosed by Turner, isexpressed by 1rD which may be considered as one wave length and thediameter at which response occurs. Referring now to FIG. 1, whichrepresents a portion of a like convolution, a conductor may be formed sothat portions are in one plane, portions 12 are in another spaced planeand portions 14 join portions 10 and 12. It will be apparent that thewave length of a convolution, formerly expressed as rrD, is nowincreased by the summation of the lengths of portions 14 contained inone convolution. (It being assumed that portions 12 are of a lengthequal to the gaps between portions 10, 10.) It follows, then, that aconvolution of one wave length will have a diameter less than D in FIG.P.A. and the overall diameter of the antenna may be reduced in someproportion to the added lengths 14, 14 in one convolution. Thus adiameter D, FIG. 1, for a convolution analogous to a convolution of FIG.P.A., is less than D of FIG. P.A. in some proportion to the addedlengths of wire 14.

DESCRIPTION OF THE PREFERRED EMBODIMENT While the invention may bepracticed with equispaced conductors, as just referred to, the spiralchosen for illustration of the preferred embodiment has conductorsegments which have a constant angle with respect to their radiusvectors. The radial spacing between adjacent conductors (say a pair 180out of phase) thus increases with increase of the radius vectors indistinction to remaining constant, as described in connection with theprior art. A spiral which cuts the radius vectors at constant angle isgenerally known as a logarithmic spiral. This is illustrated in FIG. 2wherein spiral conductors a and b have origins 180 apart and the anglebetween segment s at radius r, equals the angle between segment s atradius r etc. Since each conductor a, b, must be continuous between itsorigin near the center of the figure and its termination at theperiphery of the figure, adjacent segments of each conductor must bejoined together. This is attained in a manner similar to thatillustrated in FIG. 1 and wherein two legs 14a, 14a extend rearwardlyperpendicular to the page, one being connected to the outer end of asegment and the other to the inner end of the adjacent segment, the twolegs being connected by a bight 12a spaced rearwardly from the plane ofthe segments.

Referring now to FIG. 2, the various segments s of two conductors a andb are illustrated as they appear as viewed toward the front face of "theantenna. As illustrated, only two conductors are shown having originsand terminations 180 apart. In an actual embodiment, however, fourconductors are employed, these being disposed apart. The visiblesegments s lie on a flat dielectric plate 20 which is drilled forreceiving the rearwardly extending legs. The legs 14a, 14a pass throughsimilar holes in a rearwardly spaced conical dielectric plate 22, thebights 1201 being disposed at the rear surface of plate 22. The outerends of all conductors are connected to a ground ring 26 and their innerends are connected to terminals 28, these being connected in any wellknown manner to a source for driving the antenna, or to a receiver, ifused in such manner. The distance d between the plates constantlyincreases in a radial outward direction, thus increasing the lengths ofthe conductors between adjacent seg ments s, the distance being aconstant times a wave length. If desired, and weight is not critical,the space between the plates may be filled with a ferro-dielectricmaterial. The plates are secured to a suitable metallic cavity ring 30,closed at its rear end by a plate 32 which renders the operation of theantenna unidirectional. If

desired, the space between plates 22,32 may be filled with foam materialto render the space electrically absorbent. Any suitable mountingdevice, such as ring 34, may be employed to secure the antenna to itssupporting structure.

As will be apparent, the surface of plate is generated by a straightline rotated perpendicular to the antenna axis (planar) and the surfaceof plate 22 is generated by a straight line rotated nonperpendicular tosuch axis (cone). These surfaces may be of other shapes but normallywill be formed as surfaces of revolution of either straight lines orcurves.

What is claimed is:

l. A reduced size antenna comprising:

a dielectric planar mounting surface;

at least two substantially identical equiangularly spaced conductors;

each conductor having segmental portions lying adjacent said surface,the segmental portions forming a spiral;

said segmental portions being series connected by other portions of theconductor;

each of said other portions having a length in excess of the distancebetween ends of adjacent segments;

said other portions being disposed away from the plane of said mountingsurface;

whereby the conductor length of a convolution of the spiral is greaterthan the length around the convolution.

2. An antenna in accordance with claim 1 including a second dielectricsurface disposed in spaced relation to said mounting surface, each ofsaid other portions extending between said mounting surface and thesecond dielectric surface and each having a portion disposed adjacentand supported by the second dielectric surface.

3. An antenna in accordance with claim 2 wherein the second dielectricsurface is conical and the distance between it and the mounting surfaceconstantly increases in a radially outward direction.

4. An antenna in accordance with claim 3 wherein each of said segmentsis disposed at a constant angle to its radius vector.

1. A reduced size antenna comprising: a dielectric planar mountingsurface; at least two substantially identical equiangularly spacedconductors; each conductor having segmental portions lying adjacent saidsurface, the segmental portions forming a spiral; said segmentalportions being series connected by other portions of the conductor; eachof said other portions having a length in excess of the distance betweenends of adjacent segments; said other portions being disposed away fromthe plane of said mounting surface; whereby the conductor length of aconvolution of the spiral is greater than the length around theconvolution.
 1. A reduced size antenna comprising: a dielectric planarmounting surface; at least two substantially identical equiangularlyspaced conductors; each conductor having segmental portions lyingadjacent said surface, the segmental portions forming a spiral; saidsegmental portions being series connected by other portions of theconductor; each of said other portions having a length in excess of thedistance between ends of adjacent segments; said other portions beingdisposed away from the plane of said mounting surface; whereby theconductor length of a convolution of the spiral is greater than thelength around the convolution.
 2. An antenna in accordance with claim 1including a second dielectric surface disposed in spaced relation tosaid mounting surface, each of said other portions extending betweensaid mounting surface and the second dielectric surface and each havinga portion disposed adjacent and supported by the second dielectricsurface.
 3. An antenna in accordance with claim 2 wherein the seconddielectric surface is conical and the distance between it and themounting surface constantly increases in a radially outward direction.